Pole compensation in reconfigurable power converter

ABSTRACT

In a power converter that includes a switched-capacitor circuit connected to a switched-inductor circuit, reconfiguration logic causes the switched-capacitor circuit to transition between first and second switched-capacitor configurations with different voltage-transformation ratios. A compensator compensates for a change in the power converter&#39;s forward-transfer function that would otherwise result from the transition between the two switched-capacitor configurations.

FIELD OF DISCLOSURE This disclosure relates to power converters, and inparticular, to controlling operation of power converters. BACKGROUND

Power converters are expected to transform a first voltage into a secondvoltage. In doing so, it is necessary to control the power converter togenerate the correct second voltage in the presence of variation in thefirst voltage or in the load on the second voltage.

Control over the power converter may involve the use of feedback,thereby forming a feedback-controlled power-converter. For brevity, thiswill be referred to herein as a “controlled power-converter.” A powerconverter in the absence of feedback control will be referred to hereinas an “uncontrolled power-converter.”

Generally, overall “closed loop” response of the controlledpower-converter depends on a loop transfer-function that includes aforward transfer-function provided by the uncontrolled power-converterand a feedback transfer-function provided by one or more feedbackmodules. The combination of the two yields a closed-looptransfer-function of the controlled power-converter.

The proper design of the feedback module provides a way to controlvarious properties of the power converter's operation. For example, thefeedback transfer-function can be used to avoid instability or to adjustthe permissible gain margin or phase margin of the overall controlledpower-converter.

Needless to say, the feedback transfer-function is tightly coupled tothe forward transfer-function. If the forward transfer-function changes,it is generally necessary to also change the feedback transfer-functionto maintain desired characteristics of the controlled power-converter.This means that one cannot properly design the feedbacktransfer-function without some knowledge of the forwardtransfer-function.

Normally, this does not pose a difficulty. The forward transfer-functioncan be obtained experimentally or by inspecting the specification sheetprovided with by a manufacturer of power converters. However, thispresupposes that the forward transfer-function never changes. If itchanges significantly during operation, especially if it does so in anot entirely predictable manner, one is faced with a moving target. As aresult, it becomes difficult to suitably design a feedback module.

SUMMARY

In one aspect, the invention concerns reconfiguring a switched-capacitorcircuit of a power converter in such a way that such reconfigurationdoes not necessitate reconfiguration of at least one of the compensationcircuits used to control the power converter. In particular, theinvention concerns reconfiguring the switched-capacitor circuit of apower converter as well a first compensation circuit thereof so as toavoid having to change a second compensation circuit thereof, therebyavoiding changing the loop transfer function that is relied upon forproper feedback design. For example, the first compensation circuit,which is reconfigured along with the power converter, may be integratedwith the power converter and reconfigured by the same reconfigurationlogic that reconfigures the switched-capacitor circuit. This avoidshaving to reconfigure an external compensation circuit.

In one aspect, the invention features a compensator and reconfigurationlogic. The reconfiguration logic causes a switched-capacitor circuitthat is connected to a regulator to transition between a first andsecond switched-capacitor configurations having corresponding first andsecond voltage-transformation ratios that differ from each other. Thisresults in a change to a forward transfer function of an uncontrolledpower-converter defined by the switched-capacitor circuit and theregulator. The compensator compensates for a change in theforward-transfer function that would otherwise result from thetransition between the first and second switched-capacitorconfigurations.

In some embodiments, the reconfiguration logic reconfigures both theswitched-capacitor circuit and the compensator.

In other embodiments, when the reconfiguration logic causes theswitched-capacitor to be reconfigured, the reconfiguration logic alsocauses the compensator to be reconfigured to compensate for a changecaused by reconfiguring the switched-capacitor circuit.

In yet other embodiments, the compensator includes a first compensationcircuit that receives a voltage from a second compensation circuit.Among these are embodiments in which compensation is split between thefirst compensation circuits and a second compensation circuit thatprovides a signal to the first compensation circuit. Also among theseare embodiments in which the second compensation circuit controls gainand phase margins of a loop transfer function.

In some embodiments, the compensator compensates for a linear componentof a change in the forward-transfer function. Among these areembodiments in which the compensator includes a first compensationcircuit that compensates for a linear component of a change in theforward-transfer function and that receives a voltage from a secondcompensation circuit that compensates for a non-linear component of thechange.

In some embodiments, the compensator has a compensator transfer-functionand transitions between configurations cause a zero of the compensatortransfer-function to move in frequency steps.

Among these are embodiments in which, when the reconfiguration logiccauses the switched-capacitor circuit to transition into the secondconfiguration, a combination of the switched-capacitor circuit in thesecond configuration and the switched inductor circuit has a transferfunction that has a pole that changes frequency. In such embodiments,the reconfiguration logic causes the compensator transfer-function tohave a zero that chases the pole in frequency space.

Also among these are embodiments in which when the reconfiguration logiccauses the switched-capacitor circuit to transition into the secondconfiguration, a combination of the switched-capacitor circuit in thesecond configuration and the switched inductor circuit has a transferfunction that has a pole that has a pole frequency, wherein eachcompensator configuration defines a gap between a zero-frequencycorresponding to the configuration and the pole frequency, thezero-frequency corresponding to a frequency of a zero associated withthe compensator configuration, wherein there exists a set of gaps, eachof which corresponds to a difference between the pole frequency and azero-frequency of one of the compensator configuration, and wherein thereconfiguration logic causes the compensator transfer-function to have azero that minimizes a gap between the zero and the pole in frequencyspace.

Also among these embodiments are those in which when the reconfigurationlogic causes the switched-capacitor circuit to transition into thesecond configuration, a combination of the switched-capacitor circuit inthe second configuration and the switched inductor circuit has atransfer function that has a pole that changes frequency and wherein thereconfiguration logic causes the compensator transfer-function to have azero that has the same frequency as the pole.

Some embodiments include a first die, wherein the compensator, theswitched-capacitor circuit, and the reconfiguration logic are on thefirst die. Among these are embodiments in which the first die isconfigured to connect to a second die that contains a feedback module,the feedback module being configured to cooperate with the compensatorto provide feedback control over the uncontrolled power-converter.

Among the embodiments are those in which the uncontrolledpower-converter has a transfer function that has a first Laplacetransform that changes upon reconfiguration of the switched-capacitorcircuit and the compensator has a transfer function that has a secondLaplace transform that changes upon reconfiguration of the compensator.In these embodiments, the reconfiguration logic attempts to cause aproduct of the first and second Laplace transforms to be constant.

In some embodiments, the switched-capacitor circuit has aswitched-capacitor transfer function and the compensator has acompensator transfer function. In these embodiments, the secondswitched-capacitor configuration moves a double pole of theswitched-capacitor transfer function to a lower frequency and, inresponse, the reconfiguration logic reconfigures the compensator tolower a zero-frequency of the compensator transfer-function.

In some embodiments, the compensator and a feedback module that providesa signal to the compensator cooperate to form an adaptive compensationcircuit that dynamically responds to changes caused by reconfigurationof the switched-capacitor circuit.

A change in the forward-transfer function can result in a change in itsgain, its distribution of poles and zeros, or both. Embodiments of thecompensator include those that compensate for a change in a distributionof poles and zeros in the complex frequency domain of theforward-transfer function that would otherwise result from saidtransition between said first and second switched-capacitorconfigurations, or a change in the gain of the forward-transfer functionthat would otherwise result from said transition between said first andsecond switched-capacitor configurations, or a change in both the gainand the distribution of poles and zeros in the complex-frequency domain.

Also among the embodiments are those in which the regulator isimplemented as a switched-inductor circuit.

Additional embodiments include a comparator that receives acompensation-circuit output from the compensation circuit and areference signal, and that provides, to a modulator, a differencesignal. The modulator then provides, to the switched-inductor circuit, aduty-cycle signal with the difference signal being indicative of adifference between the reference signal and the compensation-circuitoutput and the duty-cycle signal being based on the difference signaland with the duty-cycle signal causing a change in a duty cycle of aswitch in the switched-inductor circuit. Among these embodiments arethose in which reconfiguration logic provides the modulator with anominal duty cycle and the modulator alters the nominal duty cycle inresponse to the difference signal and those in which the reconfigurationlogic provides the reference signal.

DESCRIPTION OF THE DRAWINGS These and other features and advantages ofthe invention will be apparent from the following detailed descriptionand the accompanying figures, in which:

FIG. 1 shows a control system for controlling an otherwise uncontrolledstep-up power converter;

FIGS. 2-5 show regulators for use with the power converter in FIG. 1;

FIG. 6 shows details of a reconfigurable charge-pump from the powerconverter shown in FIG. 1;

FIG. 7 shows details of an exemplary external compensation circuit fromthe control system shown in FIG. 1;

FIGS. 8 and 9 show implementations of an internal compensation circuitfrom the control system shown in FIG. 1;

FIG. 10 shows another control system for controlling the otherwiseuncontrolled step-up power converter shown in FIG. 1;

FIG. 11 shows an internal compensation circuit from the control systemshown in FIG. 10; and

FIG. 12 shows a diagram of a control system having a two-part internalcompensation circuit.

DETAILED DESCRIPTION

FIG. 1 shows a voltage source 10 that provides an input voltage VIN to acontrolled power-converter 17. The controlled power-converter 17converts the input voltage VIN into an output voltage VOUT and makes itavailable to a load 14.

A feedback control-system 16 controls the operation of an uncontrolledpower-converter 12 to yield the controlled power-converter 17. Theuncontrolled power-converter 12 defines the forward transfer-functionand the feedback control-system 16 defines its feedbacktransfer-function. The combination of the forward transfer-function andthe feedback transfer-function defines the closed-loop transfer-functionof the controlled power-converter 17.

The uncontrolled power-converter 12 includes a regulator 20 and aswitched-capacitor circuit 22. The regulator 20 and theswitched-capacitor circuit 22 connect to each other in series such thatthe regulator 20 receives the input voltage VIN and theswitched-capacitor circuit 22 provides the output voltage VOUT. In thisimplementation, regulator 20 is a boost converter. Suitable regulatorsand voltage multipliers are described in detail in U.S. Pat. No.8,817,501 and U.S. Pat. No. 9,203,299, the contents of which are hereinincorporated by reference. As used herein, the term “charge pump” refersto a switched-capacitor circuit.

The switched-inductor circuit 20 receives the input voltage VIN. It thengenerates an intermediate voltage VX and provides that intermediatevoltage VX to the switched-capacitor circuit 22. The switched-capacitorcircuit 22 then transforms the intermediate voltage VX into an outputvoltage VOUT.

Power converters of the type shown in FIG. 1 are described in detail inU.S. Pat. Nos. 8,860,396, 8,743,553, 8,723,491, 8,503,203, 8,693,224,8,724,353, 8,619,445, 9,203,299, 9,742,266, 9,041,459, U.S. PublicationNo. 2017/0085172, U.S. Patent No. 9,887,622, U.S. Pat. No. 9,882,471,PCT Publication No. WO2017161368, PCT Publication No. WO2017/091696, PCTPublication No. WO2017/143044, PCT Publication No. WO2017/160821, PCTPublication No. WO2017/156532, PCT Publication No. WO2017/196826, andU.S. Publication No. 2017/0244318, the contents of which are allincorporated herein by reference.

FIG. 2 shows the regulator 20 implemented as a switched-inductor circuitthat receives an input voltage across its first and secondregulator-terminals 41, 42. A switched-inductor controller 40 attemptsto regulate this input voltage to provide a steady output voltage acrossits third and fourth regulator-terminals 43, 44. The switched-inductorcontroller 40 attempts to maintain a steady output voltage by changing aduty cycle of a regulator-switch 46, thereby selectively disconnectingand connecting an inductance 48.

The particular embodiment shown in FIG. 2 is a buck converter. The samecomponents but rearranged into a different topology yield a boostconverter in FIG. 3 and a buck-boost converter in FIG. 4. In analternative embodiment shown in FIG. 5, a transformer provides both theinductance 48 and galvanic isolation between the first and secondregulator-terminals 41, 42 and the third and fourth regulator-terminals43, 44. The illustrated topology in FIG. 5 defines a fly back converter.The regulators shown in FIGS. 2-5 all feature a switch 46 thatselectively connects and disconnects an inductance 48, thereby enablingvoltage regulation. Other suitable regulators, which are not shown,include Cuk converters, SEPIC converters, resonant converters,multi-level converters, Forward Converters, and Full-Bridge Converters.

FIG. 6 shows an example of a switched-capacitor circuit 22 for use inthe uncontrolled power-converter 12 of FIG. 1.

The switched-capacitor circuit 22 is a single-phase step-up symmetriccascade multiplier having first, second, third, fourth, and fifthstack-switches S₁, S₂, S₃, S₄, S₅, and first, second, third, and fourthphase switches S₆, S₇, S₈, S₉ that cooperate to receive an input voltageacross first and second switched-capacitor terminals 61, 62 and toproduce an output voltage across third and fourth switched-capacitorterminals 63, 64.

There are four sets of switches: the first, third, and fifthstack-switches S₁, S₃, S₅ define a set of “odd stack-switches”; thesecond and fourth stack-switches S₂, S₄ define a set of “evenstack-switches;” the first and third phase switches S₆, S₈ define a setof “even phase-switches” and the second and fourth phase-switches S₇, S₉define a set of “odd phase-switches.”

The switched-capacitor circuit 22 also includes first, second, third,and fourth capacitors C₁, C₂, C₃, C₄. Together with the switches, thesedefine “stages” within the switched-capacitor circuit 22.

The illustrated switched-capacitor circuit 22 has four stages. Eachstage includes one of the capacitors C₁, C₂, C₃, C₄ and one of fourcorresponding stack-switches S₁, S₂, S₃, S₄. The first stage includesthe first stack-switch Si and the first capacitor C₁; the second stageincludes the second stack-switch S₂ and the second capacitor C₂; thethird stage includes the third stack-switch S₃ and the third capacitorC₃; and the fourth stage includes the fourth stack-switch S₄ and thefourth capacitor C₄. In the embodiment shown in FIG. 3, the maximumvoltage-transformation ratio is five because there are four stages.

In response to receiving control signals on a switched-capacitor controlterminal 65, a charge-pump controller 66 places operationcontrol-signals on a control-signal path 60. These operationcontrol-signals cause the first, second, third, fourth, and fifthstack-switches S₁, S₂, S₃, S₄, S₅ and the first, second, third, andfourth phase switches S₆, S₇, S₈, S₉ to change states according to aspecific sequence. As a result, the switched-capacitor circuit 22repeatedly transitions between first and second operating-states at aspecific frequency.

For example, during a first operating-state, the charge-pump controller66 closes the odd stack-switches S₁,, S₃, S₅ and the odd phase-switchesS₇, S₉ and opens the even stack-switches S₂, S₄ and the even phaseswitches S₆, S₈. In contrast, during a second operating-state, thecharge-pump controller 66 opens the odd stack-switches S₁, S₃, S₅ andthe odd phase-switches S₇, S₉ and closes the even stack-switches S₂, S₄and the even phase-switches S₆, S₈.

In addition, the charge-pump controller 66 transmits reconfigurationcontrol-signals to a reconfiguration input terminal B1 of areconfiguration block 68. In response, the reconfiguration block 68provides reconfiguration signals at its reconfiguration output terminalsA₁-A₃. These reconfiguration signals alter the connections between thecapacitors C₁-C₄ in the first and second operating-state.

The switched-capacitor circuit 22 has switches that open and close inthe normal course of operation. The act of opening and closing theseswitches does not amount to changing the mode. The term“reconfiguration” expressly excludes the opening and closing of theseswitches during normal operation and is for the purpose of causing aselected voltage-transformation ratio.

The ability to reconfigure the connections between the capacitors C₁-C₄is particularly advantageous because it means that the same circuitrycan be used to implement different voltage-transformation ratios.However, this ability comes at a cost. In particular, when thereconfiguration block 68 reconfigures the connections, it also changesthe control system's forward transfer-function. Such a change can bemanifested as a change in the forward transfer-function's gain, a changein its distribution of its poles and zeros in the complex-frequencydomain, or both.

Other examples of charge pumps include Ladder, Dickson, Series-Parallel,Fibonacci, and Doubler, all of which can be adiabatically charged andconfigured into multi-phase or single-phase networks. A particularlyuseful charge pump is an adiabatically charged version of a full-wavecascade multiplier. However, diabatically charged versions can also beused.

As used herein, changing the charge on a capacitor “adiabatically” meanscausing at least some of the charge stored in that capacitor to changeby passing it through a non-capacitive element. A positive adiabaticchange in charge on the capacitor is considered adiabatic charging whilea negative adiabatic change in charge on the capacitor is consideredadiabatic discharging. Examples of non-capacitive elements includeinductors, magnetic elements, resistors, and combinations thereof.

In some cases, a capacitor can be charged adiabatically for part of thetime and diabatically for the rest of the time. Such capacitors areconsidered to be adiabatically charged. Similarly, in some cases, acapacitor can be discharged adiabatically for part of the time anddiabatically for the rest of the time. Such capacitors are considered tobe adiabatically discharged.

Diabatic charging includes all charging that is not adiabatic anddiabatic discharging includes all discharging that is not adiabatic.

As used herein, an adiabatically charged switched-capacitor circuit is aswitched-capacitor circuit having at least one capacitor that is bothadiabatically charged and adiabatically discharged. A diabaticallycharged switched-capacitor circuit is a switched-capacitor circuit thatis not an adiabatically charged switched-capacitor circuit.

Referring back to FIG. 1, an external compensation circuit 18 receivesthe output voltage VOUT as a feedback signal and transforms it into afirst compensation voltage VCOMP. An internal compensation circuit 26compares this first compensation voltage VCOMP with a reference voltageVREF.

The external compensation circuit 18 is typically provided by the enduser based on the particular details of the application. However, as canbe seen in FIG. 1, the external compensation circuit 18 has no way toknow if reconfiguration has occurred. As such, the external compensationcircuit 18 would have no way to compensate for any changes to the systemtransfer function that would be wrought by such reconfiguration.

The internal compensation circuit 26, on the other hand, is an integralpart of the uncontrolled power-converter 12. The internal compensationcircuit 26 is regarded as “internal” because it is ordinarily on thesame semiconductor die as one or more other components of theuncontrolled power-converter 12. In contrast, the external compensationcircuit 18 would connect to but be external to such a semiconductor die.

As such, it receives a signal indicative of a reconfiguration event andcompensates for changes to the system transfer function that result,whether the change manifests itself as a change in the transferfunction's gain or a change in its distribution of its poles and zeros.This relieves the end user from having to know when theswitched-capacitor circuit 22 has been reconfigured.

Based on this comparison between the compensation voltage VCOMP with areference voltage VREF, the internal compensation circuit 26 outputs asecond compensation voltage VCOMP2.

Accordingly, the external compensation circuit 18 and the internalcompensation circuit 26 define a multi-stage compensation circuit thatcooperate to stabilize the overall control system.

In the illustrated embodiment, reconfiguration logic 24 provides thereference voltage VREF. However, it is also possible to provide thereference voltage VREF from an external source.

Referring now to FIG. 7, the external compensation circuit 18 transformsthe output voltage VOUT, which can be relatively high, into a lowerfirst compensation voltage VCOMP. Having a lower compensation voltageavoids having to provide circuitry within the internal compensationcircuit 26 that would be required to sustain high voltages.

To accomplish this, the external compensation circuit 18 features avoltage divider having first and second resistors RD1, RD2 that define anode to which the internal compensation circuit 26 can be connected toreceive the first compensation voltage VCOMP.

The external compensation circuit 18 also features a reactive path inparallel with the first resistor RD1. In the illustrated embodiment, thereactive path features a reactive-path resistor RPO and a reactive-pathcapacitor CZO in series. By choosing the values of the reactive path'sresistance and capacitance, it is possible to modify the system transferfunction by introducing a pole and a zero at a particular location inthe complex plane.

FIGS. 8 and 9 show two embodiments of the internal compensation circuit26.

In the first embodiment, shown in FIG. 8, an operational amplifier 27receives the first compensation voltage VCOMP and the reference voltageVREF at its inverting and non-inverting inputs respectively. This causesthe second compensation voltage VCOMP2 at the operational amplifier'soutput. An optional feedback path between the operational amplifier'soutput and its inverting input includes a feedback resistor RZ2 and afeedback capacitor CP2. These introduce a pole and a zero into thesystem transfer function. By choosing the resistance of the feedbackresistor RZ2 and/or the feedback capacitor CP2, it is possible tocontrol the location of the pole and zero in the complex-frequencydomain.

In the second embodiment, shown in FIG. 9, an operational transimpedanceamplifier 27 receives the first compensation voltage VCOMP and thereference voltage VREF at its inverting and non-inverting inputsrespectively. This causes the second compensation voltage VCOMP2 at theoperational transimpedance amplifier's output. An optional shunt pathbetween the operational transimpedance amplifier's output and groundincludes a shunt resistor RZ1 and a shunt capacitor CP1. These introducea pole and a zero into the system transfer function. By choosing theresistance of the shunt resistor RZ1 and/or the shunt capacitor CP1, itis possible to control the location of the pole and zero in thecomplex-frequency domain.

Referring back to FIG. 1, a modulator 28 receives the secondcompensation voltage VCOMP2 and uses it to generate a duty-cycle signalD that is then passed to the switched-inductor controller 40 through theswitched-inductor circuit's control terminal 45. The switched-inductorcontroller 40 uses this duty-cycle signal D as a basis for controllingthe duty cycle of the regulator-switch 46 in the switched-inductorcircuit 20.

In some embodiments, the reconfiguration logic 24 uses the input voltageVIN and the desired output voltage VREF to output a nominal duty-cyclesignal D0. In these embodiments, the second compensation voltage VCOMP2causes the modulator 28 to modify the nominal duty-cycle signal D0 togenerate the duty-cycle signal D. In those embodiments in which thecircuitry that generates the forward transfer-function isreconfigurable, the nominal duty-cycle signal D0 depends onconfiguration and may therefore change upon reconfiguration of thatcircuitry. For example, in those embodiments in which thevoltage-transformation ratio of the switched-capacitor circuit 22 can bechanged, the nominal duty-cycle signal D0 will change in a correspondingmanner.

The duty-cycle signal D affects the duty cycle, and hence the currentpassing out of the switched-inductor circuit 20. In general, thiscurrent increases with duty cycle. However, the relationship betweenduty cycle and current depends on the details of the switched-inductorcircuit 20. The net result in either case is that the output voltageVOUT tracks the reference voltage VREF.

The feedback loop is designed to achieve certain desired operationalcharacteristics of the controlled power-converter 17. These can includecapping the steady-state difference between the output voltage VOUT andthe reference voltage VREF as well as the dynamic response of the outputvoltage VOUT to disturbances, such as step changes or oscillations atvarious frequencies in either the input or output currents. Ofparticular importance is that the feedback loop be configured to ensurethat the output voltage VOUT tracks the reference voltage VREF.

The external compensation circuit 18 is not necessarily required foroperation of the power converter. In some cases, there is a directconnection so that the output voltage VOUT is equal to the compensationvoltage VCOMP. In this scenario, the resistors and reactive elements canbe moved from the external compensator circuit 18 to the internalcompensation circuit 26.

Among those configurations that use feedback are those in which theexternal compensation circuit 18 implements a low-pass filter having along time-constant. This promotes stability of the overallfeedback-controlled power-converter 17.

Other configurations that use feedback have an external compensationcircuit 18 that provides desired response to perturbations, such asrapid changes in load current, that may result in corresponding rapidchanges in the output voltage VOUT.

The compensation voltage depends on the feedback transfer-function,which itself assumes a particular forward transfer-function. If theforward transfer-function changes, then the compensation voltage willchange.

FIG. 10 shows a power converter similar to that shown in FIG. 1 but withthe reconfiguration logic 24 also having the ability to reconfigure theswitched-capacitor circuit 22 in response to the input and outputvoltages VIN, VOUT of the power converter. Such reconfiguration has theeffect of changing the voltage-transformation ratio, which in turnchanges the forward-path transfer function.

The change in the forward-path transfer function changes the overalldynamics of the controlled power-converter 17. These changes may affectthe response of the output voltage VOUT to variations in the inputvoltage VIN or the output current IOUT. Thus, if the externalcompensation circuit 18 were designed for use with a first configurationof the switched-capacitor circuit 22, it would be quite possible that itwould no longer work as expected when the switched-capacitor circuit 22assumes its second configuration.

To accommodate this difficulty, the controlled power-converter 17 alsofeatures a reconfigurable internal compensation circuit 30 that receivesa first compensation voltage VCOMP from the external compensationcircuit 18 and transforms it into a second compensation voltage VCOMP2that depends on the configuration of the switched-capacitor circuit 22.Thus, when the reconfiguration block 68 in FIG. 6 reconfigures theswitched-capacitor circuit 22, the reconfiguration logic 24 alsoreconfigures the reconfigurable internal compensation circuit 30. Thecombination of the reconfigurable internal compensation circuit 30 andthe external compensation circuit 18, when present, can be viewed as anadaptive compensation circuit that dynamically responds toreconfiguration events within the circuitry that generates the forwardtransfer-function.

The reconfigurable internal compensation circuit 30 compensates for someor all of the changes in the forward transfer-function. In particular,the reconfigurable internal compensation circuit 30 causes the overallforward transfer-function to appear to stay the same, even though thereconfiguration block 68 may have reconfigured the switched-capacitorcircuit 22. In a case where the feedback control is based on lineartransfer functions, which can be characterized by their Laplacetransforms, this can be achieved by ensuring that the product of theLaplace transform of the uncontrolled power-converter's transferfunction, which is the combined transfer functions of the switchedinductor-circuit 20 and the switched-capacitor circuit 22, and theLaplace transform of the feedback control-system 16 remain constant.

In some embodiments, this can be carried out by moving poles and/orzeros of the switched-capacitor circuit's transfer function in thecomplex-frequency domain with corresponding poles and/or zeros of thereconfigurable compensator's transfer function. However, in cases wherethis is difficult to execute, it is possible to provide heuristic rulesfor moving the poles and/or zeros of the reconfigurable compensator'stransfer function. For example, if the switched-capacitor circuit'svoltage-transformation ratio increases, then an output double-pole willtypically move to a lower frequency. To compensate for this, thereconfiguration logic 24 will reconfigure the reconfigurable internalcompensation circuit 30 to have its zeros at a lower frequency as well.

In this embodiment, the reconfiguration logic 24 changes the location ofthe zeros of the reconfigurable internal compensation circuit 30 insteps. As an example, a reconfigurable internal compensation circuit 30may be configured to move its zeros in steps of 50 kHz. In that case,the uncontrolled power-converter 12 may begin operating with a doublepole at 100 kHz, in which case the reconfigurable internal compensationcircuit 30 would be set to have a zero at 100 kHz. However, if uponreconfiguration the uncontrolled power-converter 12 now has a pole at 30kHz, it is not possible for the reconfigurable internal compensationcircuit 30 to place a corresponding zero at 30 kHz. In that case, thereconfigurable internal compensation circuit 30 would do the best it canby placing a zero at the closest permissible location in frequencyspace, namely at 50 kHz.

Referring to FIG. 11, the reconfigurable internal compensation circuit30 includes an operational transimpedance amplifier (“OTA”) 35 thatreceives the first compensation voltage VCOMP and the reference voltageVREF at its inverting and non-inverting inputs respectively. An optionalshunt path between the operational transimpedance amplifier's output andground includes a shunt resistor RZ3 and a shunt capacitor CP3. Theseintroduce a pole and a zero into the system transfer function, thelocation of which depends on the choice of resistance and capacitance.To provide the flexibility of moving poles and zeroes it is possible forone or both of the shunt resistor RZ3 and the shunt capacitor CP3 topresent a variable electrical parameter. In the illustrated embodiment,the shunt resistor RZ3 has a variable resistance and the shunt capacitorCP3 has a variable capacitance. There are numerous ways to electricallycontrol the resistance of the shunt resistor RZ3 and the capacitance ofthe shunt capacitor CP3.

The output of the operational transimpedance amplifier 35 is not used asthe second compensation voltage VCOMP2, as was the case in FIG. 9.Instead, it is passed into an optional reconfigurable active zerocircuit 33.

The reconfigurable active zero circuit 33 is a network of resistiveelements R_(X), R_(Y), R_(Z), and reactive elements C_(A), C_(B), C_(C),C_(D) interconnected by switches S_(A), S_(B), S_(C), S_(X), S_(Y),S_(Z). By selectively opening and closing combinations of switches, itis possible to move the zero location, thereby compensating for themovement of poles and zeroes upon reconfiguration of theswitched-capacitor circuit 22.

In some embodiments, the capacitors C_(A), C_(D), C_(C), C_(D) haveequal capacitances and the resistors R_(X), R_(Y), R_(Z) have equalresistances. But this is by no means required. In addition, there is noparticular constraint on how many capacitors and resistors are present.The choice of values and numbers depends primarily on how many statesthe switched-capacitor circuit 22 is reconfigurable into and where thepoles and zeroes introduced by such reconfigurations will be in thecomplex plane.

The reconfiguration logic 24 further includes logic for choosing whichof the switches S_(A), S_(B), S_(C), S_(X), S_(Y), S_(Z) to open andclose to achieve the required compensation in response to theswitched-capacitor circuit's reconfiguration. The choice is such thatthe uncontrolled power-converter 12 presents a nominal forwardtransfer-function. This nominal forward transfer-function is lessdependent on the switched-capacitor circuit's reconfiguration than itwould have been in the absence of the reconfigurable internalcompensation circuit 30.

As a result of always presenting the same nominal transfer function, itis not necessary to reconfigure the external compensation circuit 18 toaccommodate reconfiguration of the switched-capacitor circuit 22. Thismeans that the switched-capacitor circuit 22 is able to change itsvoltage-transformation ratio in a relatively seamless way, at least asseen from outside the power converter 10. The reconfigurable internalcompensation circuit 30 thus makes the overall transfer-function lessdependent on any reconfiguration of the switched-capacitor circuit 22than it would be if the reconfigurable internal compensation circuit 30were not present. More generally, the reconfigurable internalcompensation circuit 30 renders the overall transfer-function lessdependent on any reconfiguration of any portion of the circuitry that isresponsible for changing the forward transfer-function than it would beif the reconfigurable internal compensation circuit 30 were not present.

In some embodiments, the reactive elements are capacitors. It ispossible that the resistive and reactive elements are small enough sothat the reconfigurable internal compensation circuit 30, theswitched-capacitor circuit 22, and the reconfiguration logic 24 are onthe same semiconductor die. The external compensation circuit 18 can beon a different die and/or created using external components such asmultilayer ceramic capacitors (MLCCs) and chip resistors.

In FIG, 12, the modulator 28, the switched-inductor circuit 20, and theswitched-capacitor circuit 22 have been combined to form a switchedregulator 34. As indicated by the dashed arrows, the reconfigurationlogic 24 reconfigures both the switched regulator 34 and thereconfigurable internal compensation circuit 30.

In the embodiment shown, the output of the switched regulator 34 is theoutput voltage VOUT. The inputs to the switched regulator 34 are thesecond compensation voltage VCOMP2, the input voltage VIN, and theoutput current LOUT. The second compensation voltage VCOMP2 is afunction of the first compensation voltage VCOMP, an input referencevoltage VREF, and/or other values.

For a particular configuration of the reconfigurable internalcompensation circuit 30, the design of the external compensation circuit18 depends on a loop transfer function of a loop that begins with theswitched regulator 34, proceeds through an additional internalcompensation circuit 38.

The additional internal compensation circuit 38 typically includescircuitry for introducing poles and zeros into the transfer function. Insome embodiments, the poles and zeros are fixed. In other embodiments,the poles and zeros are reconfigurable. In either case, the externalcompensation circuit 18 receives the output of the additional internalcompensation circuit 38.

In some embodiments, the external compensation circuit 18 includes avoltage divider as shown in FIG. 7. However, in other embodiments, theadditional internal compensator circuit 38 includes such a voltagedivider instead.

The reconfigurable internal compensation circuit 30 receives thisreduced voltage VCOMP and proceeds to dynamically introduce additionalpoles and zeros as discussed in connection with FIG. 9 or 11.

The design of the external compensation circuit 18 relies on the gainand phase margins of the loop transfer function. The gain and phase ofthe loop-transfer function are, in general, functions of frequency. Ingeneral, there will exist a frequency at which the phase is equal to 180degrees relative to a reference. At that frequency, there will also be acorresponding gain. The extent to which this corresponding gain is lessthan unity, measured in dB, is the “gain margin.”

Conversely, since the gain and phase both depend on frequency, therewill be a frequency at which the gain is unity. The corresponding phaseat that frequency is what determines phase margin. In particular, thephase margin is the extent to which that corresponding phase falls shortof 180 degrees.

In some examples, the gain and phase response of the feedback controlsystem 16 are modeled as small signals that are susceptible tolinearized analysis around an operating point of the switched regulator34.

In some cases, the task of compensating for linear and non-linearproperties of the feedback control system 16 is split between thereconfigurable internal compensation circuit 30 and the externalcompensation circuit 18. In some embodiments, the reconfigurableinternal compensation circuit 30 compensates for the linear component ofthe overall transfer function whereas the external compensation circuit18 compensates for the non-linear component and vice versa.

Generally speaking, a computer accessible storage medium may include anynon-transitory storage media accessible by a computer during use toprovide instructions and/or data to the computer. For example, acomputer accessible storage medium may include storage media such asmagnetic or optical disks and semiconductor memories.

Generally, a non-abstract database representative of the system may be adatabase or other data structure that can be read by a program and used,directly or indirectly, to fabricate the hardware comprising the system.For example, the database may be a behavioral-level description orregister-transfer level (RTL) description of the hardware functionalityin a high-level design language (HDL) such as Verilog or VHDL. Thedescription may be read by a synthesis tool that may synthesize thedescription to produce a netlist comprising a list of gates from asynthesis library. The netlist comprises a set of gates that alsorepresent the functionality of the hardware comprising the system. Thenetlist may then be placed and routed to produce a data set describinggeometric shapes to be applied to masks. The masks may then be used invarious semiconductor fabrication steps to produce a semiconductorcircuit or circuits corresponding to the system. In other examples,Alternatively, the database may itself be the netlist (with or withoutthe synthesis library) or the data set.

Having described the invention, and a preferred embodiment thereof, whatis claimed as new and secured by letters patent is:

1-20. (canceled)
 21. An apparatus comprising: a controller to generate one or more control signals; and a compensator to compensate for a change in a gain of a power converter based, at least in part, on the one or more control signals, the gain is to be based, at least in part, on a transition between a first and a second power converter configurations to correspond to a first and a second voltage transformation ratios, wherein the change in the gain to include a change in at least one transfer function of the power converter, and wherein the compensator to compensate for the change in the at least one transfer function to occur based, at least in part, on the transition between the first and the second power converter configurations.
 22. The apparatus of claim 21, wherein the power converter to include at least a charge pump and a regulator to be coupled to the charge pump.
 23. The apparatus of claim 22, wherein the first and the second power converter configurations to comprise configurations with respect to the charge pump and/or the regulator.
 24. The apparatus of claim 21, wherein the at least one transfer function to comprise at least one forward transfer function.
 25. The apparatus of claim 21, wherein the first and the second voltage transformation ratios to be different from each other.
 26. The apparatus of claim 21, wherein the power converter to comprise a buck-boost power converter.
 27. The apparatus of claim 21, wherein the compensator to compensate for one or more linear properties of the change in the at least one transfer function.
 28. The apparatus of claim 27, wherein the compensator to comprise a first compensation circuit to compensate for one or more linear properties of a change in the at least one transfer function, the first compensation circuit to receive a voltage from a second compensation circuit, the second compensation circuit to compensate for one or more non-linear properties of the change.
 29. The apparatus of claim 21, wherein the at least one transfer function to include a compensator transfer function, a zero of the compensator transfer function to move in frequency steps to be based, at least in part, on the transition between the first and the second power converter configurations.
 30. The apparatus of claim 29, wherein the second power converter configuration to include a transfer function with a pole that is to change frequency, and wherein the compensator transfer function to include a zero that is to chase the pole in an associated frequency space.
 31. The apparatus of claim 29, wherein the second power converter configuration to include a transfer function with a pole to include a pole frequency, wherein the second power converter configuration to include a compensator configuration to define a gap between a zero frequency corresponding to the compensator configuration and the pole frequency, the zero frequency to correspond to a frequency of a zero to be associated with the compensator configuration.
 32. The apparatus of claim 31, wherein the compensator configuration to further define a set of gaps, a particular gap of the set of gaps to correspond to a difference between the pole frequency and a zero frequency of at least one of the compensator configuration, and wherein the compensator transfer function to have a zero so as to minimize a gap between the zero and the pole in an associated frequency space.
 33. The apparatus of claim 29, wherein the second power converter configuration to include a transfer function with a pole that is to change frequency, and wherein the compensator transfer function to include a zero to have the same frequency as the pole.
 34. The apparatus of claim 21, wherein the at least one transfer function to include at least a charge pump transfer function and a compensator transfer function, wherein, with the power converter in the second power converter configuration, a double pole of the charge pump transfer function to move to a lower frequency.
 35. The apparatus of claim 34, wherein the compensator to lower a zero frequency of the compensator transfer function based, at least in part, on the move of the double pole of the charge pump to the lower frequency.
 36. The apparatus of claim 21, wherein the compensator to compensate for the change in the gain to include a compensation in a change in a distribution of poles and zeros in a frequency domain of the at least one transfer function to occur based, at least in part, on the transition between the first and the second power converter configurations.
 37. The apparatus of claim 21, wherein the compensator to comprise an internal compensation circuit and an external compensation circuit to be coupled to the internal compensation circuit, the internal compensation circuit to receive a voltage from the external compensation circuit, and wherein the compensation for the change in the gain to be split between the internal compensation circuit and the external compensation circuit, the internal compensation circuit to compensate for one or more linear properties of the at least one transfer function and the external compensation circuit to compensate for one or more non-linear properties of the at least one transfer function.
 38. A method for compensating for a change in a gain of a power converter, the method comprising: detecting a transition between a first and a second power converter configurations corresponding to a first and a second voltage transformation ratios of the power converter, determining a change in at least one transfer function of the power converter based, at least in part, on the detected transition; generating one or more control signals based, at least in part, on the determined change; and compensating for the change in the at least one transfer function resulting from the transition between the first and the second power converter configurations based, at least in part on the one or more control signals.
 39. The method of claim 38, wherein compensating for the change in the at least one transfer function between the first and the second power converter configurations comprises compensating for configurations with respect to a charge pump and/or a regulator of the power converter.
 40. The method of claim 38, wherein the power converter to comprise a buck-boost power converter, wherein the at least one transfer function comprises at least one forward transfer function, and wherein the first and the second voltage transformation ratios are different from each other. 